The centre of the image below shows a photodiode made by the Fraunhofer FEP institution with a transparent electrode of graphene that allows ultraviolet light to reach the photodiode. The jars of fluorescent dye in the background show that ultraviolet (UV) light is in use, and the current meter on the right shows that the photodiode is able to detect this light.This particular photodiode is made from organic materials (rather than e.g. silicon) and so can be cheaply made by processes similar to printing, eventually on a flexible polymer substrate, allowing low production costs. Graphene is advantageous for this application because it is flexible, UV-transparent and very flat (this latter property may enable lower backgrounds for organic photodiodes (OPDs) from the so-called ‘dark current’).
Such UV-sensitive photodiodes with graphene electrodes have been successfully tested as fire sensors (UV smoke detection system) within the GLADIATOR project by the partner Organic Electronic Technologies, which also designed and fabricated the electronic circuit board to support their operation, as can be seen in the video below: